That's sea ice extent, not measuring the ice sheet (which is the permanent glacier on land).

Also it's well within the historical variability, so probably not a huge flag right now.. Might be worth checking over the next few weeks though. Antarctic sea ice did fall off a cliff over the last decade.. There's also an El Niño building, which is connected to warming I'm the Amundsen Sea, though I don't know how the timing works there.